This invention relates generally to heat exchangers and, more specifically, to a header apparatus for a tube-in-tube heat exchanger.
The most common type of heat pump is one wherein heat is either transferred to or from a refrigerant by way of a heat exchanger which has ambient air flowing thereover. Such a system is sometimes referred as an air source heat pump since it is the condition of the ambient air which is applied to change the temperature of the refrigerant. In a similar manner, where there is a source of water, such as a pond or the like, which can be used to temper the condition of a refrigerant, a so called water source heat pump is used to cool or heat the refrigerant by way of a heat exchanger having water flowing therethrough.
Typically, such a water-to-refrigerant heat exchanger is in the form of a so called tube-in-tube heat exchanger wherein a single or a plurality of inner tubes are disposed in an outer tube, and the liquid and the refrigerant are made to flow through the respective outer and inner tubes, or vise versa, such that heat transfer is effected across the radial dimensions of the inner tube(s). In order to maintain a separation between the liquid and the refrigerant in such a system, it is common to provide a header for the purpose of defining a common boundary between the liquid and the refrigerant flow circuits and for holding the ends of the inner tubes. Heretofore, this has been accomplished by the use of a intermediate plate, separate from the header body, to function as the separator/manifold between the water and the refrigerant. In order to secure this intermediate plate within the header body, it was first necessary, with some difficulty, to install it into the desired position, and then to secure it in that position. Gas welding or flame brazing was typically used to braze the plate in place. Either of these approaches tends to heat a large amount of material, thus requiring more brazing alloy and larger headers to prevent alloy reflow. That is, where two distinct brazed joints are located in close physical proximity, unless they can be brazed simultaneously, the brazing of the second joint will tend to cause a melting of the braze of the first joint. And even when they can be brazed simultaneously, if thin wall tubing is being used, one must avoid the prolonged holding of the metal at the brazing temperature since it can compromise the strength of the metal. Since flame brazing requires longer times at the brazing temperature, the inner tubing is generally required to have relatively thick walls so as to consistently obtain highly reliable joints. While there is thus a need for relatively thick walled tubing, it is recognized that thin walled inner tubing is desirable because it offers improvements in heat transfer characteristics, cost and weight.
In addition to the difficulty in brazing thin walled tubes as discussed hereinabove, it is also recognized that the relative thicknesses of the elements being brazed (i.e. the thickness of the tubes and the thickness of the plate) should be comparable. That is, if the plate is thick and the tubes are thin, it is very difficult to get consistent and strong brazed joints throughout. Further, if the thickness of the plate is reduced so as to accommodate the thin walled tubing, then the strength of the thin walled plate under high pressures may not be sufficient to prevent deformation of the plate, which in turn may cause failure of the tubes.
It is, therefore, an object of the present invention to provide an improved header structure for a tube-in-tube heat exchanger.
Another object of the present invention is the provision for reducing the difficulty of installing the separator/manifold member in a tube-in-tube heat exchanger header.
Yet another object of the present invention is the provision for a tube-in-tube heat exchanger which can accommodate the use of relatively thin walled inner tubes.
Still another object of the present invention is the provision for a tube-in-tube heat exchanger which allows the use of both thin walled tubes and a relatively thin separator/manifold member without causing tube failure under higher pressure operation.
Yet another object of the present invention is the provision in a tube-in-tube heat exchanger for preventing tube failure when the separator/manifold member flexes under higher pressures.
Still another object of the present invention is the provision for a tube-in-tube heat exchanger header which is economical to manufacture and practical and effective in use.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.